Question: $ D = \left[\begin{array}{rrr}0 & 2 & 2 \\ 2 & 1 & 2 \\ 1 & 0 & 0\end{array}\right]$ What is $ D^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}0 & 0 & 1 \\ 1 & -1 & 2 \\ -\frac{1}{2} & 1 & -2\end{array}\right]$